This invention relates to a parallax free sight, comprising an elongated light channel, with a concave-convex lens attached to one end of the light tunnel. On the concave side, there is a layer reflecting light of certain wave lengths. A transparent body is attached to the other end of the light channel, and a light emitting means is arranged in the focal point of the concave part of the lens between said lens and the transparent body. The light channel is intended to follow movements of an object to be aimed at by said sight.
Different types of optical fire arms sights are frequently utilized in both hunting and military applications to improve targeting accuracy. The most frequently used type are telescopic sights, provided with a cross-hair in the lens system, which comprises a tube or a light channel. However, recently parallax free sights or reflex sights, which preferably do not enlarge the image, and have aiming marks shaped as a spot or a ring have become more common. A major advantage with the latter type and sight is that the aiming spot does not have to be centered in the sight when aiming the sight and weapon. Thus, the aiming step is more rapid and safe. Another large advantage, is that the sight does not enlarge. Only one eye has to be directed through the sight while the other can be kept open and directed also towards the target or target area, whereby the gunner increases substantially the general view of the target area.
Sights free of parallax are based on the principal of a concave-convex lens having a semi-reflective layer on the concave side of the lens. The sight is arranged to be moved with and adjustable to the barrel of the fire arm, said concave and reflecting side of the lens being directed towards the eye of the gunner. Normally the sight is mounted on a rail on the barrel and adjustable by means of adjustment screws or the like. The lens is also mounted in relation to the sight line of the gunner through the lens so that the focal point of the semi-reflective layer on the concave side of the lens is somewhat below the sight line. A light beam is directed at the aiming mark so that it is reflected off the lens in the direction of the eye of the gunner. The light beams reflected from the semi-reflective layer are parallel due to the construction of the lens. The aiming mark appears to the gunner as distant or at infinity. As the target normally is also distant from the gunner, both the target and the aiming mark can be focused at the same time, whereby the gun is readily and accurately directed towards the target. This type of sight is disclosed in the U.S. Pat. No. 4,346,995.
Previously used lenses, e.g., according to the above-mentioned patent, were normally provided with spherical shaped optical surfaces resulting in an optical error in the lens, in the form of a relatively large spherical aberration. To some extent, this type of error can be compensated by using so-called double lenses which during some ideal circumstances may give a reflection free from said error. Due to the fact that the lens in practice is always arranged at an angle other than a right angle in relation to the sight line, some spherical aberration still remains, even with double lenses.
In the military area and also in the hunting area the most common targets, which are not stationary, move horizontally. Sights according to previously known technique having circular cross section are thus constructed with a large radius so as to accomplish an acceptable aiming area in the horizontal direction. Thereby such sights are comparatively large and, as the aiming mark is arranged in or close to the center of the sight, the distance or offset between the sightline and the shooting line is large, which is disadvantageous. A large distance results, if the gun is inclined so that a line between the sightline and the shooting line differs from a vertical line, in that the calibration in relation to the actual trajectory will not be correct.
To achieve as large a contrasting effect as possible between the aiming mark and target, the aiming mark is illuminated, normally by a light emitting diode or a similar device. Other types of luminous aiming marks comprise illuminous material.
As guns suitable for this type of sight are indeed portable, the supply of power to the light emitting diode causes some problems. Normal types of batteries are of course used, but in reality such batteries are either small and have low capacity or are large and are difficult to place, as well as being heavy. The batteries must be well protected against rain and moisture and should also be easy to replace. These two features are difficult to combine.
Rechargeable batteries are also used, but the state of charge of such batteries must be checked carefully before the sight is used so that the function of the sight has not deteriorated due to use. Any charging of the battery must be taken care of before using the sight, while practical problems exist when charging in connection with the actual use of the sight.